Liquid crystal display apparatuses are widely used as the large-sized displays of flat-screen televisions and monitors, etc. These liquid crystal display apparatuses employ a backlight unit that applies illuminating light to a liquid crystal display panel from the back or the lower side of the liquid crystal display panel to enhance the luminance of the display screen.
The backlight unit has a lightguide plate and a light source comprising, for example, a plurality of light-emitting diodes (LEDs) disposed along one side edge surface of the lightguide plate. The lightguide plate receives light from the LED light source, guides the light through the lightguide plate and emits the guided light from the whole light-exiting surface of the lightguide plate toward a liquid crystal display panel.
Recently, as liquid crystal televisions increase in size, backlight units used therein have been demanded to further reduce in weight and thickness. In this regard, there have been some problems to be solved. As the thickness of a lightguide plate constituting a backlight unit is reduced, it becomes likely that color irregularity and luminance unevenness will occur in light emitted from the lightguide plate. If injection molding is employed as a method of producing a large-sized lightguide plate, it is difficult to fill the resin material throughout the molding tool for the large lightguide plate. Increasing the injection pressure can solve this problem, which, however, causes an increase in installation cost. Extrusion molding can produce large-sized and thin lightguide plates but cannot appropriately form microscopic optical configurations on the lightguide plates.
Meanwhile, there have been developed planar light-emitting devices in which a plurality of lightguide plates are arranged side by side with their respective upper surfaces as light-exiting surfaces being flush with each other and a plurality of light sources are provided in association with the lightguide plates to obtain a wide light-exiting surface (see Japanese Patent Application Publication Nos. 2007-293339 and Hei 11-288611).
In the planar light-emitting device disclosed in Japanese Patent Application Publication No. 2007-293339, however, a light source for emitting light into one rectangular lightguide plate through a light-entrance surface, which is one end edge surface of the lightguide plate, is set in a cut portion formed in an opposing end edge surface of another lightguide plate adjacent to the one lightguide plate. Therefore, a part of light emitted from the light source may leak out upward through a gap between the respective end edge surfaces of the mutually adjacent lightguide plates, causing bright lines to appear undesirably. In the planar light-emitting device disclosed in Japanese Patent Application Publication No. Hei 11-288611, one of the opposing end edge portions of each pair of mutually adjacent lightguide plates is reduced in thickness, and the other end edge portion is provided with a step-shaped recess that receives the thinned end edge portion, thereby allowing the opposing end edge portions to overlap each other. With this structure, however, light emitted from an associated light source is reflected upward at the overlapping portions, causing bright lines undesirably.